systemd-user: start lal-application-end.target on stop/restart
We have a problem that SIGSTOP'ed apps don't get the memo when Lomiri stops for any reason, causing the apps (and subsequently the LAL units) to linger around, confusing LAL and causing those apps to not be launch-able again.
Together with [1], make sure those apps are ended when Lomiri ends through the use of lal-application-end.target. This restores the functionality in the Upstart unit file.
Fixes: lomiri-app-launch#14 (closed) Fixes: lomiri-app-launch#16 (closed)